Low-voltage circuit breakers which switch in air require an arc quenching device for operation, in order to quench arcs that occur without any adverse effect on the circuit breaker itself or on adjacent system parts or other assemblies. This is because if this is not done, there is a risk of the hot and hence ionized arc gases causing electrical flashovers, injuring operators, or causing other damage.
Two fundamentally different physical forms are known for the conventional arc quenching devices for low-voltage circuit breakers. In large circuit breakers, until now, complete quenching chambers, which are essentially conventionally produced separately as a component, that is to say a robust enclosure which is resistant to arcs, pressure and temperature and has arc splitters located in it, and a suitable blowing apparatus have until now been fitted to the circuit breaker. One quenching chamber is generally provided for each pole. This chamber has a complete enclosure whose strength is matched not only to the mechanical forces but also to the electrical forces of the arc which occurs in it and is to be quenched, in particular with regard to the pressure and the temperature of the switching gases. The arc splitters are located in this chamber. The chamber may in this case be in the form of a pot-like shaft in which the splitter plates are inserted, or in the form of a structure composed of half shells in which an apparatus is required in order firstly to insert the splitter plates into one half shell, then to fit the second half shell, and finally to connect the two half shells.
Quenching chamber inserts are used as a second form, in which only the function of actual arc quenching can be achieved in one unit. However, this design is not able to withstand the pressure which occurs in conjunction with the arc. These inserts are therefore inserted into a shaft which is provided in or on the switch enclosure. Until now, this form has been predominantly used for small compact circuit breakers, but is also increasingly being used for relatively large circuit breakers, where the enclosures surround these areas, that is to say the switching area and the quenching area.
In these modern low-voltage circuit breakers, the arc quenching chambers are integrated in the enclosure of the switch. The quenching chambers therefore do not form an object projecting beyond the contour of the switch. Although, as before, they are autonomous objects for large circuit breakers, they are, however, included in the overall design such that they end flush with the enclosure contours and only the outlet openings are still visible. However, the parts are accessible and can be removed in order, for example, to assess the contacts located underneath them. If necessary, the entire quenching chamber can also be replaced.
In certain types of even relatively large low-voltage circuit breakers, which are referred to by the American expression ICCB (insulated case circuit breaker), such a design has already been chosen in which prefabricated arc splitter stacks are inserted into the switch enclosure. However, this results in a secondary problem. The insertion of the arc splitter stack does not yet in itself complete the arc quenching device as an entity since, in the end, the switching gases have to leave the switch and emerge into free space without being able to cause any damage.
In conventional circuit breakers, outlet openings are provided for this purpose in the enclosure, which are a component of the enclosure, for example a perforated wall in the enclosure or a wire grating inserted into a retaining opening in the enclosure. This is necessary since, after passing through the arc splitter stack, the switching gasses have not yet been sufficiently cooled down to allow them to emerge into free space. The gas is hot and ionized, and this can lead to flashovers to grounded parts or between busbars. The hot switching gases may also cause sparks and can endanger or injure operators. In consequence, further cooling is essential. Further chamber attachments have therefore been created. For example, DE-A 35 41 514 and 44 10 108 disclose a completely autonomous structure, although based on conventional arc quenching chambers, with enclosure bodies and arc splitters arranged in them, with damping apparatuses fitted to the quenching chambers in order to further cool the switching gases, which are still too hot having passed through the splitter plates, with the damping apparatus that is proposed in DE A 44 10 108 being in the form of an isolating fitted chamber cover, and DE A 35 41 514 indicating a solution in which the attachment contains a number of perforated inserts which are held by means of a covering element through which attachment elements pass. This attachment is highly complex in terms of design and manufacture and has only a partial influence on the characteristics.
A damping insert that is provided also requires a specific pressure response. The gases must emerge unimpeded from the arc splitter area and must then be trapped in a temporary storage area from which, in the end, they can emerge into free space, after having been cooled down.
There are situations in which this solution is not adequate either. EP PS 0437151 B1 discloses a multiple low-voltage circuit breaker in a dielectric enclosure which is equipped with a duplicated cooling apparatus for the quenching gases and is subdivided by dielectric intermediate walls into a number of internal compartments, each of which is associated with one of the poles. In this case, each switching pole has an associated arc splitter stack for deionization of the arc that is struck when the contacts are disconnected, as well as an outlet opening, which is fitted with a first gas cooling apparatus, for the switching gases. These outlet openings then open into a further chamber, which is shared by all the switch poles and has a second cooling apparatus, after passing through which the switching gases are dissipated through gas outlet openings into the surrounding medium. The gases, which are still very hot and are still highly ionized, meet one another before the second cooling apparatus, which can lead to disadvantages.
None of the cited solutions have any damping or blowing devices which themselves belong to only a single arc quenching chamber. They thus represent a comparatively high level of complexity both with regard to the amount of material and with regard to the extent of assembly work. Furthermore, they do not allow the use of uncomplicated material-saving quenching chamber designs, since these do not sufficiently damp and cool down the emerging switching gases.
Furthermore, they do not effectively prevent the still hot, ionized switching gases from entering areas of the switchgear assembly in which they can cause damage. For this reason, known circuit breakers are then subject either to a restricted voltage range or, as described, additional parts such as chimneys or attachments with deionizing media are used. This may be the situation when an increased short-circuit switching capacity is required or a higher rated voltage, for example a higher short-circuit current, since this in general leads to the quenching chamber having to have a larger volume because these parameters affect the design of the quenching chamber, for example the number of arc splitters, the length of the distance which the arc can travel on the arc splitters, the nature of the insulation, damping or deionization at the output of the quenching chamber, and other features.
The chimneys or attachments which have been mentioned are, however, always designed for only one specific situation and cannot be used, extended, varied, interchanged or replaced universally.